Thin-film magnetic head having ensured insulation between shield and magnetic detecting element

ABSTRACT

A thin-film magnetic head has a lower shield layer and an upper shield layer which are each composed of two layers of a first shield sub-layer and a second shield sub-layer. The second shield sub-layer has a specific resistance higher than that of the first shield sub-layer. Thus, even though the gap length become shorter, the second shield sub-layers and gap layers ensure electrical insulation, and therefore, an electrically insulative thin-film magnetic head can be achieved.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to thin-film magnetic heads inwhich shield layers are disposed on gap layers on both surfaces of amagnetic detecting element. In particular, the present invention relatesto a thin-film magnetic head in which the insulation between the shieldlayers and the magnetic detecting element can be ensured and which hasexcellent heat dissipation performance and the shield layers havingimproved soft-magnetic characteristics.

[0003] 2. Description of the Related Art

[0004]FIG. 8 is a fragmentary sectional view of a known thin-filmmagnetic head when viewed from a side opposing a recording medium.

[0005] The thin-film magnetic head has a lower shield layer 1 formed of,for example, a NiFe alloy and a lower gap layer 2 formed of, forexample, Al₂O₃ on the lower shield layer 1.

[0006] As shown in FIG. 8, a magnetic detecting element 3 is formed onthe lower gap layer 2. The magnetic detecting element 3 has a hard biaslayer 5 and an electrode layer 6 which are formed on both sides of amultilayer film 4 in the track width direction.

[0007] The magnetic detecting element 3 is a spin-valve thin-film sensorin which the multilayer film 4 is composed of, for example, anantiferromagnetic layer, a pinned magnetic layer, a nonmagneticconductive layer, and a free magnetic layer.

[0008] An upper gap layer 7 is formed of, for example, Al₂O₃ on themagnetic detecting element 3 and an upper shield layer 8 is formed of,for example, a NiFe alloy on the upper gap layer 7.

[0009] As the demand for a high recording density is increasing, thedistance between the shield layers 1 and 8, that is, a gap length GI,becomes shorter to achieve a narrower gap. In order to achieve a narrowgap, the thicknesses of the lower gap layer 2 and the upper gap layer 2need to be reduced.

[0010] For example, if the recording density increases to 70 Gbit/in²from 40 Gbit/in², the gap length G1 between the shield layers 1 and 8must be reduced to about 600 Å.

[0011] In this instance, if the thickness of the magnetic detectingelement 3 is about 200 Å or more, the thicknesses of the lower gap layer2 and the upper gap layer 7 must be about 200 Å or less.

[0012] However, if the lower gap layer 2 and the upper gap layer 7 havesuch a small thickness, they are liable to have pin holes, thus causingpoor insulation between the magnetic detecting element 3 and the shieldlayers 1 and 8.

[0013] Poor insulation between the electrode layer 6 of the magneticdetecting element 3 and the upper shield layer 8 readily causes a shortcircuit between the electrode layer 6 and the upper shield layer 8, andthis prevents an increase of reading output of the magnetic detectingelement 3.

[0014] On the other hand, as the recording density is increased, themagnetic detecting element 3 more radiates heat. Accordingly, the heatmust be conducted to the shield layers 1 and 8; hence, the gap layers 2and 7 must have excellent heat dissipation performance.

[0015] Also, the shield layers 1 and 8 need to have a shielding functionfor absorbing an external magnetic field or noise to prevent theexternal magnetic field from affecting the magnetic detecting element 3.The shield layers 1 and 8, therefore, must be soft magnetic.

SUMMARY OF THE INVENTION

[0016] Accordingly, an object of the present invention is to provide athin-film magnetic head in which the insulation performance between theshield layers and the magnetic detecting element can be ensured andwhich has an excellent heat dissipation performance and the shieldlayers having improved soft magnetic characteristics.

[0017] To this end, according to one aspect of the present invention,there is provided a thin-film magnetic head. The thin-film magnetic headincludes a magnetic detecting element. Gap layers are disposed on bothsurfaces of the magnetic detecting element. Shield layers are eachdisposed on the corresponding gap layer. The magnetic detecting elementside of at least one shield layer has a higher specific resistance thanthat of the other side.

[0018] For example, the shield layers each comprise a first shieldsub-layer and a second shield sub-layer. The second shield-sub-layer isdisposed on the corresponding gap layer and has a specific resistancehigher than that of the first shield sub-layer.

[0019] The second shield sub-layers are electrically insulative due tothe high specific resistance thereof. The electrical insulation of thethin-film magnetic head is, therefore, ensured by the gap layers and thesecond shield sub-layers. Thus, even if the thickness of the gap layersand the gap length become smaller, the insulation between the magneticdetecting element and the first shield sub-layers can be improved.

[0020] Also, by forming the second shield sub-layers with a thin filmcapable of ensuring electrical insulation, a heat dissipating thin-filmmagnetic head can be achieved. In this magnetic head, even if thetemperature of the magnetic detecting element increases as the currentdensity is higher according to increase of the recording density, heatcan be released through the gap layers and the second shield sub-layersto the first shield sub-layers.

[0021] For example, the second shield sub-layers are formed of amagnetic material having a specific resistance higher than that of thefirst shield sub-layers. Hence, the second shield sub-layers which areformed of the magnetic material serve as shields as well as the firstshield sub-layers.

[0022] In the present invention, therefore, the gap length G1 depends onthe total thickness of the magnetic detecting element and the lower gaplayers. Even though the gap length becomes smaller according to thedemand for higher recording density, the second shield sub-layers canhave a shielding function and improved electoral insulation performance.

[0023] Preferably, the first shield sub-layer and the second shieldsub-layer are in contact with each other, thus generating aferromagnetic bonding therebetween. Even if the second shield sub-layershave relatively worse soft magnetic properties such as magneticpermeability, the ferromagnetic bonding allows the soft magnetic firstshield sub-layers to improve the soft magnetic characteristics of thesecond shield sub-layers. Thus, the second shield sub-layers can serveas adequate shield layers.

[0024] By forming the second shield sub-layers of a magnetic materialhaving-a high specific resistance, a thin-film magnetic head can beachieved which have improved electoral insulation performance and animproved shielding function provided by both the first shield sub-layersand the second shield sub-layers.

[0025] The total thickness of the second shield sub-layer and the gaplayer adjoining the second shield sub-layer may be in the range of 100to 500 Å. Thus, a thin-film magnetic head having improved electricalinsulation performance and excellent heat dissipation performance can beachieved.

[0026] Preferably, the total thickness is in the range of 100 to 200 Å.Thus, the present invention can be adapted event though the gap lengthis reduced to increase the recording density to 70 Gbit/in² from 40Gbit/in².

[0027] Preferably, the thickness of the second shield sub-layer is inthe range of 20 to 200 Å.

[0028] More preferably, the thickness of the second shield sub-layer isin the range of 20 to 100 Å.

[0029] Preferably, the thickness of the first shield sub-layer is in therange of 5×103 Å to 3 μm.

[0030] By setting the thicknesses of the first shield sub-layers and thesecond shield sub-layers in the above-described ranges, the electricalinsulation performance and the heat dissipation performance can beimproved.

[0031] Preferably, the second shield sub-layer comprises a magneticoxide.

[0032] Specifically, the second shield sub-layer may comprise a Mn—Znferrite or a Ni—Zn ferrite.

[0033] Since such a magnetic oxide has a high specific resistance, thesecond shield sub-layers can have improved electrical insulationperformance while having improved soft magnetic characteristics to serveas shield layers in association with the first shield sub-layers due tothe ferromagnetic bonding between the first shield sub-layers and thesecond shield sub-layers.

[0034] The second shield sub-layer may comprise a magnetic materialrepresented by Fe_(a)M_(b)O_(c). M is at least one element selected fromthe group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo., Si, P, C, W, B, Al,Ga, Ge, and rare earth elements, and a, b, and c representing atomicratios satisfy the relationships of 50≦a≦70, 5≦b≦30, 10≦c≦30, and a+b+c=100.

[0035] The second shield sub-layers may comprise a magnetic materialrepresented by (Co_(1-g)T_(g))_(x)M_(y)L_(z)O_(w). T is Fe or Ni. M isat least one element selected from the group consisting of Ti, Zr, Hf,Nb, Ta, Cr, Mo, Si, P, C, W, B, Al, Ga, Ge, and rare earth elements; Lis at least one element selected from the group consisting of Au, Ag,Cu, Ru, Rh, Os, Ir, Pt. and Pd; g representing an atomic ratio satisfiesthe relationship of 0≦g≦0.7; y, z, and w representing atomic ratiossatisfy the relationships of 3≦y≦30, 0≦z ≦20, 7≦w≦40, and 20≦y+z+w≦60;and x represents the atomic ratio of the balance.

[0036] The second shield sub-layer may comprise a magnetic materialrepresented by Fe_(d)M_(e)N_(f). M is at least one element selected fromthe group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B, Al,Ga, Ge, and rare earth elements, and d, e, and f representing atomicratios satisfy the relationships of 60≦d≦80, 10≦e≦15, 5<f≦30, and d+e+f=100.

[0037] The magnetic materials described above have a high specificresistance, and can have a specific resistance of, for example, 10 ⁴μΩ·cm can be achieved depending on the composition ratio of thematerials. By using the magnetic materials for the second shieldsub-layers, therefore, the electrical insulation performance can beimproved. In addition, the ferromagnetic bonding between the first andsecond shield sub-layers allows the first shield sub-layers to improvethe soft magnetic characteristics of the second shield sub-layers, andthus the second shield sub-layers can serve as shield layers inassociation with the first shield sub-layers. The materials for thesecond shield sub-layers are not limited to the above, but may be anymagnetic material having a high specific resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a fragmentary sectional view of a thin-film magnetichead according to a first embodiment of the present invention whenviewed from a side opposing a recording medium;

[0039]FIG. 2 is a fragmentary sectional view of a thin-film magnetichead according to a second embodiment of the present invention whenviewed from a side opposing a recording medium;

[0040]FIG. 3 is a fragmentary sectional view of a thin-film magnetichead according to a third embodiment of the present invention whenviewed from a side opposing a recording medium;

[0041]FIG. 4 is a fragmentary sectional view of a thin-film magnetichead according to a fourth embodiment of the present invention whenviewed from a side opposing a recording medium;

[0042]FIG. 5 is a fragmentary sectional view of a magnetic detectingelement according to an embodiment of the present invention when viewedfrom a side opposing a recording medium;

[0043]FIG. 6 is a fragmentary sectional view of a magnetic detectingelement according to another embodiment of the present invention whenviewed from a side opposing a recording medium;

[0044]FIG. 7 is a fragmentary sectional view of a magnetic detectingelement according to another embodiment of the present invention whenviewed from a side opposing a recording medium; and

[0045]FIG. 8 is a fragmentary sectional view of a known thin-filmmagnetic head when viewed from a side opposing a recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046]FIG. 1 is a fragmentary sectional view of a thin-film magnetichead according to a first embodiment of the present invention whenviewed from a side opposing a recording medium.

[0047] The thin-film magnetic head shown in FIG. 1 is a read head (MRhead) for reading external signals and is formed on an end of a floatinghead slider thereof.

[0048] In the present invention, a recording inductive head may beformed above the read head. The inductive head has core layers and acoil layer. The reference numeral 21 in FIG. 1 designates an uppershield layer, and the upper shield layer 21 may serve as a lower corelayer of the inductive head as well as serving as a shield. The lowercore layer, alternatively, may be formed individually and is separatedfrom the upper shield layer 21 by an insulating layer.

[0049] The reference numeral 10 designates a first lower-shieldsub-layer. The first lower-shield sub-layer 10 is formed of a magneticmaterial, such as a NiFe alloy (permalloy), a FeAlSi alloy (sendust), aCoFe alloy, or a CoFeNi alloy.

[0050] In order to serve as an excellent shield, the first lower-shieldsub-layer 10 must have soft magnetic properties, such as a high magneticpermeability, a high saturation magnetic flux density, and a lowcoercive force. The above-described magnetic materials have these softmagnetic properties. Preferably, the first lower-shield sub-layer 10 hasa magnetic permeability of 500. The specific resistance of the firstlower-shield sub-layer 10 is very low and is several μΩ·cm.

[0051] A second lower-shield sub-layer 12 is formed of a material havinga specific resistance higher than that of the first lower-shieldsub-layer 10 on the first lower-shield sub-layer 10.

[0052] A lower gap layer 13 is formed of a general insulating material,such as Al₂O₃ or SiO₂, on the second lower-shield sub-layer 12.

[0053] A magnetic detecting element 14 is formed on the lower gap layer13. In this embodiment, the magnetic detecting element 14 is composed ofa multilayer film 15, which is shown in the center of the drawing, and ahard bias layer 16 and an electrode layer 17 formed on both sides of themultilayer film 15 in the X direction. The multilayer film 15 has agiant magnetoresistive structure (GMR structure) or an anisotropicmagnetoresistive structure (AMR structure), a tunnel magnetoresistivestructure, or the like. The structure of the multilayer film 15 will bemore specifically described later.

[0054] An upper gap layer 18 is formed of an insulating material, suchas Al₂O₃ or SiO₂, on the magnetic detecting element 14, like the lowergap layer 13.

[0055] A second upper-shield sub-layer 19 and a first upper-shieldsub-layer 11 are formed on the upper gap layer 18, in that order. Thesecond upper-shield sub-layer 19 has a specific resistance higher thanthat of the first upper-shield sub-layer 11.

[0056] The first upper-shield sub-layer 11 is formed of a magneticmaterial, such as a NiFe alloy (permalloy), a FeAlSi alloy (sendust), aCoFe alloy, or a CoFeNi alloy, like the first lower-shield sub-layer 10.

[0057] Functions of the second shield sub-layers 12 and 19, will now bedescribed. The lower shield layer 20, which is separated from themagnetic detecting element 14 by the lower gap layer 13, is composed oftwo layers of the first lower-shield sub-layer 10 and the secondlower-shield sub-layer 12, as shown in FIG. 1.

[0058] The upper shield layer 21, which is separated from the magneticdetecting element 14 by the upper gap layer 18, is also composed of twolayers of the first upper-shield sub-layer 11 and the secondupper-shield sub-layer 19.

[0059] The second lower-shield sub-layer 12 and the second upper-shieldsub-layer 19 are formed of a magnetic material having a specificresistance higher than that of the first lower-shield sub-layer 10 andthe first upper-shield sub-layer 11, respectively.

[0060] In order to achieve a high recording density, the gap length G1,which depends on the total thickness of the magnetic detecting element14, the lower gap layer 13, and the upper gap layer 18, must be small.When the recording density is 40 to 70 Gbit/in², for example, the gaplength G1 must be 600 Å or less.

[0061] As the gap length G1 becomes smaller, the thicknesses of thelower and upper gap layers 13 and 18 must be much smaller accordingly.As a result, the insulation between the gap layers 13 and 18 and theshield layers 20 and 21 is liable to be degraded. In order to solve thisproblem, in the present invention, the highly resistive second shieldsub-layers 12 and 19 are provided in the respective shield layers 20 and21 so as to oppose to the gap layers 13 and 18. Thus, the second shieldsub-layers 12 and 19 as well as the gap layers 13 and 18 areelectrically insulative.

[0062] Thus, sensing current flowing from the electrode layer 17 to themultilayer film 15 rarely diverges into the shield layers 20 and 21 tocause a current loss.

[0063] In addition, the second shield sub-layers 12 and 19, which areformed of a magnetic material, serve as shield layers as well as thefirst shield sub-layers 10 and 11.

[0064] The second shield sub-layers 12 and 19, of which the materialwill be specifically described later, must have a specific resistancehigher than that of the first shield sub-layers 10 and 11, but does notnecessarily have other advantageous characteristics. For example, softmagnetic characteristics including magnetic permeability of the secondshield sub-layers 12 and 19 may be worse than those of the first shieldsub-layers 10 and 11.

[0065] Preferably, the first shield sub-layers 10 and 11 are directly incontact with the second shield sub-layers 12 and 19, respectively, toform a ferromagnetic bonding between the first shield sub-layers 10 and11 and the second shield sub-layers 12 and 19, as shown in FIG. 1.

[0066] This ferromagnetic bonding allows the soft-magnetic first shieldsub-layers 10 and 11 to improve the soft magnetic characteristics of thesecond shield sub-layers 12 and 19, even if the second shield sub-layers12 and 19 alone have worse soft magnetic characteristics.

[0067] Thus, the second shield sub-layers 12 and 19 not only serve asinsulating layers with the gap layers 13 and 18, but also serve asshield layers with the first shield sub-layers 10 and 11.

[0068] The thicknesses of the first shield sub-layers 10 and 11 and thesecond shield sub-layers 12 and 19 will now be described.

[0069] In the present invention, preferably, the total thickness of thesecond lower-shield sub-layer 12 and the adjoining gap layer 13 and thetotal thickness of the second upper-shield sub-layer 19 and theadjoining gap layer 18 are in the range of 100 to 500 Å.

[0070] According to the present invention, even if the gap layers 13 and18 become thinner to achieve a high recording density, insulationperformance can be increased by setting the total thicknesses t5 and t6within the above-described range.

[0071] Total thicknesses t5 and t6 more than 500 Å further increaseinsulation performance, but unfortunately, they lower heat dissipationperformance.

[0072] The heat dissipation performance depends on the thermalconductivity of the gap layers 13 and 18 and the second shieldsub-layers 12 and 19. A high thermal conductivity promises high heatdissipation performance and vice versa.

[0073] The gap layers 13 and 18 are generally formed of Al₂O₃, which hasa relatively low thermal conductivity, or the like. On the other hand,the second shield sub-layers 12 and 19 are formed of an FeMO alloydescribed latter or the like in which an amorphous phase containsmicrocrystalline phases.

[0074] While a high crystallinity leads to an increased thermalconductivity, presence of the amorphous phase readily lowers the thermalconductivity. Hence, the gap layers 13 and 18 and the second shieldsub-layers 12 and 19 have relatively low thermal conductivities. If thetotal thicknesses t5 and t6 of the gap layers 13 and 18 and the secondshield sub-layers 12 and 19 become larger, the heat dissipation fromthese layers is likely to decrease accordingly. The total thicknesses t5and t6 are, therefore, set to 500 Å or less in the present invention.

[0075] In the present invention, by setting the total thicknesses t5 andt6 within the range of 100 to 200 Å, a narrow-gap thin-film magnetichead having a recording density of 40 to 70 Gbit/in² can be achieved.

[0076] Preferably, the thicknesses t1 and t2 of the second shieldsub-layers 12 and 19 are in the range of 20 to 200 Å.

[0077] If the thicknesses t1 and t2 are smaller than 20 Å, theinsulation performance of the second shield sub-layers 12 and 19 israpidly degraded, and thus the insulation between the magnetic detectingelement 14 and the first shield sub-layers 10 and 11 cannot be ensured.

[0078] If the thicknesses t1 and t2 are larger than 200 Å, theinsulation performance of the second shield sub-layers 12 and 19 isfavorable. However, the heat dissipation of the thin-film magnetic headis degraded, and the shielding function of the second shield sub-layers12 and 19 is degraded because of lowered soft magnetic characteristicsthereof.

[0079] As described above, the ferromagnetic bonding between the firstshield sub-layers 10 and 11 and the second shield sub-layers 12 and 19improves the soft magnetic characteristics of the second shieldsub-layers 12 and 19. If the thicknesses t1 and t2 of the second shieldsub-layers are larger than 200 Å, however, the soft magneticcharacteristics of the second shield sub-layers 12 and 19 cannot beimproved, and thus the second shield sub-layers 12 and 19 cannotadequately serve as shields.

[0080] The thicknesses t1 and t2, therefore, are set within the range of20 to 200 Å.

[0081] More preferably, the thicknesses t1 and t2 are in the range of 20to 100 Å. In this instance, the total thicknesses t5 and t6 of thesecond shield sub-layers 12 and 19 and the gap layers 13 and 18 may beset within the range of 100 to 200 Å.

[0082] Preferably, the thicknesses t3 and t4 of the first shieldsub-layers 10 and 11 are in the range of 5×10³ Å to 3 μm.

[0083] If the thicknesses t3 and t4 are less than 5×10³ Å, the shieldingfunction of the first shield sub-layers 10 and 11 is unpleasantlydegraded.

[0084] While large thicknesses t3 and t4 of the first shield sub-layers10 and 11 improve the shielding function thereof, thicknesses t3 and t4larger than 3 μm increase surface roughness, and thus make it difficultto form layers on the first shield sub-layers 10 and 11.

[0085] The thicknesses t3 and t4 of the first shield sub-layers 10 and11 are, therefore, set within the range of 5×103 Å to 3 μm in thepresent invention.

[0086] Preferably, the ratios of the thicknesses t1 and t2 to therespective thicknesses of the shield layers 20 and 21, that ist1/(t1+t3) and t2/(t2+t4), are in the range of 6.5×10⁻⁴ to 4×10^(−2.)Thus, the insulation performance and the soft magnetic characteristicsof the second shield sub-layers 12 and 19 are improved, and the heatdissipation performance of the thin-film magnetic head is improved.

[0087] The second shield sub-layers 12 and 19 are formed of thefollowing material.

[0088] In the present invention, preferably, the second shieldsub-layers 12 and 19 are formed of a magnetic oxide.

[0089] (1) Mn—Zn ferrite or Ni—Zn ferrite Since Mn—Zn and Ni—Zn ferriteshave high specific resistances, the insulation performance of the secondshield sub-layers 12 and 19 can be improved. Also, the ferromagneticbonding between the first shield sub-layers 10 and 11 and the secondshield sub-layers 12 and 19 improves the soft magnetic characteristicsof the second shield sub-layers 12 and 19, and thus the second shieldsub-layers 12 and 19 can effectively serve as shield layers inassociation with the first shield sub-layers 10 and 11.

[0090] (2) Magnetic oxides represented by Fe_(a)M_(b)O_(c)

[0091] M represents at least one element selected from the groupconsisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B, Al, Ga, Ge,and rare earth elements, and a, b, and c representing atomic ratiossatisfy the relationships of 50≦a≦70, 5≦b≦30, 10≦c≦30, and a+b+c=100.

[0092] FeMO alloys having this composition ensure a specific resistanceof 400 to 2×105 μΩ·cm.

[0093] (3) Magnetic oxides represented by(Co_(1-g)T_(g))_(x)M_(y)L_(z)O_(w)

[0094] T represents Fe or Ni; M represents at least one element selectedfrom the group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B,Al, Ga, Ge, and rare earth elements; L represents at least one elementselected from the group consisting of Au, Ag, Cu, Ru, Rh, Os, Ir, Pt,and Pd; g representing an atomic ratio satisfies the relationship of0≦b≦0.7; y, z, and w representing atomic ratios satisfy therelationships of 3≦y≦30, 0≦z≦20, 7≦w≦40, and 20≦y+z+w≦60; and xrepresents the atomic ratio of the balance.

[0095] (COT)MLO alloys having this composition ensure a specificresistance of several thousand μΩ·cm.

[0096] Instead of magnetic oxides, the second shield sub-layers 12 and19 may be formed of the following magnetic materials.

[0097] (4) Magnetic materials represented by Fe_(d)M_(e)N_(f)Mrepresents at least one element selected from the group consisting ofTi, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B, Al, Ga, Ge, and rare earthelements, and d, e, and f representing atomic ratios satisfy therelationships of 60≦d≦80, 10≦e≦15, 5≦f≦30, and d+e+f=100.

[0098] FeMN alloys having this composition ensure a specific resistanceof 400 to 2×105 μΩ·cm.

[0099] Since the magnetic materials (2) to (4) comprise an amorphousphase containing a large amount of oxides or nitrides of the element Mand microcrystalline phases mainly containing Fe or mainly containingthe element T and Co, the amorphous phase provably have a high specificresistance.

[0100] The second shield sub-layers 12 and 19 may be formed of materialsother than the magnetic materials described above. Preferably, thematerials used for the second shield sub-layers 12 and 19 have aspecific resistance of 1000 μΩ·cm or more.

[0101] Characteristics of the second shield sub-layers 12 and 19 willnow be described.

[0102] As mentioned above, preferably, the second shield sub-layers 12and 19 have a specific resistance of 1000 μΩ·cm or more, and morepreferably of 1×10⁴ μΩ·cm Such a specific resistance leads to improvedinsulation performance of the second shield sub-layers 12 and 19, andthus a thin-film magnetic head having excellent insulation performancecan be achieved, even though the gap length becomes shorter.

[0103] Preferably, the magnetic permeability μ of the second shieldsub-layers 12 and 19 is more than 200 or more when they are combinedwith the respective first shield sub-layers 10 and 11.

[0104] Specifically, the individual magnetic permeability μof the secondshield sub-layers 12 and 19 may be lower than 200. By combining thesecond shield sub-layers 12 and 19 with the first shield sub-layers 10and 11, the ferromagnetic bonding between the first shield sub-layers 10and 11 and the second shield sub-layers 12 and 19 increases the magneticpermeability μto the range of 200 to 2000.

[0105] Thus increased magnetic permeability leads to an improvedshielding function of the second shield sub-layers 12 and 19.

[0106] Preferred materials for the lower gap layer 13 and the upper gaplayer 18 will now be described.

[0107] As mentioned above, the lower gap layer 13 and the upper gaplayer 18 are formed of a general insulating material, such as Al₂O₃ orSiO₂, of which the thermal conductivity is relatively low. Preferably,the lower gap layer 13 and the upper gap layer 18 are formed of aninsulative and thermal-conductive material. Increasing the thermalconductivity of the lower gap layer 13 and the upper gap layer 18 leadsto an improved heat dissipation performance.

[0108] Preferably, the lower gap layer 13 and the upper gap layer 18 areformed of at least one insulating material selected from the groupconsisting of AlN, AlSiN, AlSiO, SiC, diamond like carbon (DLC), BN,MgO, SiAlON, AlON, Si₃N₄, SiCO, SiN, SiON, and SiCON. These materialshave a thermal conductivity higher than that of Al₂O₃, which is used forconventional gap layers.

[0109] A process of preparing the second shield sub-layers 12 and 19will now be described.

[0110] Preferably, the second shield sub-layers 12 and 19 are formed bysputtering with an existing system, such as an RF diode, an RF triode,an ion beam, and a facing target sputtering system. By forming thesecond shield sub-layers 12 and 19 by sputtering, the second shieldsub-layers 12 and 19 can have thicknesses t1 and t2 in the preferredrange described above, which must be smaller than those of the firstshield sub-layers 10 and 11.

[0111] Alternatively, the second shield sub-layers 12 and 19 may beformed by vapor deposition, molecular beam epitaxy (MBE), ionizedcluster beam (ICB), or the like.

[0112] In this sputtering process, the second shield sub-layers 12 and19 are deposited with the above-described material, such as FeMO, usedas a target, thus having a substantially uniform composition.

[0113] Alternatively, the second shield sub-layers 12 and 19 may beformed with a plurality of targets. For example, an Fe target, an ironoxide target, and a target comprising an oxide of the element M areused.

[0114] By supplying constant power to each target, the second shieldsub-layers 12 and 19 can be deposited with a substantially uniformcomposition.

[0115] Also, power supply to these three targets may be changed. Forexample, when the second upper-shield sub-layer 19 is formed, more poweris applied to the iron oxide target and the element M-oxide target inthe early stage to increase the oxygen content of the early-stage layer.Thus, the second upper-shield sub-layer 19 has an adequately highspecific resistance in the early stage. Then, power supply to the Fetarget is gradually increased. As a result, the oxygen content of thesurface of the second upper-shield sub-layer 19 decreases gradually and,in contrast, the Fe content increases while the surface is moving awayfrom the magnetic detecting element 14.

[0116] By changing the amount of power supply when a plurality oftargets are used, the oxygen content of the second shield sub-layers 12and 19 can be changed according to the distance from the magneticdetecting element 14.

[0117] The second shield sub-layers 12 and 19 must be electricallyinsulative particularly at under surface side of the lower gap layer 13and the upper surface side of the upper gap layer 18. As the distancefrom the magnetic detecting element 14 is getting shorter, the oxygencontent of the second shield sub-layers 12 and 19 increases gradually,and accordingly, the specific resistance thereof become higher. Thus,the electrical insulation performance of the gap layers 13 and 18 andthe second shield sub-layers 12 and 19 can be efficiently increased.Also, since the Fe content of the second shield sub-layers 12 and 19gradually increases as the distance from the magnetic detecting element14 is getting longer, the soft magnetic characteristics thereof can beensured at the sides opposing the first shield sub-layers 10 and 11. Bycombining the second shield sub-layers 12 and 19 with the first shieldsub-layers 10 and 11, ferromagnetic bonding is generated therebetween.The ferromagnetic bonding allows the soft magnetic first shieldsub-layers 10 and 11 to improve the soft magnetic characteristics of thesecond shield sub-layers 12 and 19. In addition, if the second shieldsub-layers 12 and 19 have soft magnetic characteristics in the sidesopposing the first shield sub-layers 10 and 11 when they are formed, thesoft magnetic characteristics can be further improved by the softmagnetic first shield sub-layers 10 and 11 with the ferromagneticbonding therebetween.

[0118] Also, it is expected that the amount of microcrystalline phasesof the second shield sub-layers 12 and 19 increases and, in contrast,the amount of amorphous phase decreases as the Fe content is increasing.Accordingly, if the Fe content of the second shield sub-layers 12 and 19is increased as the distance from the magnetic detecting element 14 isgetting longer, it is expected that the heat dissipation performance ofthe second shield sub-layers 12 and 19 can be improved.

[0119] A second embodiment will now be described with reference to FIG.2. The same layers are designated by similar numerals.

[0120] The thin-film magnetic head of the second embodiment has the samestructure as that of the first embodiment except for the lower shieldlayer.

[0121] While the lower shield layer 20 of the first embodiment iscomposed of the first lower-shield sub-layer 10 and the secondlower-shield sub-layer 12 having a specific resistance higher than thatof the first lower-shield sub-layer 10, the lower shield layer of thesecond embodiment is composed of only the first shield sub-layer 10.

[0122] On the other hand, the upper shield layer 21 is composed of twolayers of the first upper-shield sub-layer 11 and the secondupper-shield sub-layer 19 having a specific resistance higher than thatof the first upper-shield sub-layer 11, like the first embodiment.

[0123] In the second embodiment, the electrode layer 17 of the magneticdetecting element 14 is opposed to the upper shield layer 21 with thegap layer 18 therebetween. The electrical insulation, therefore, needsto be ensured particularly between the electrode layer 17 and the uppershield layer 21.

[0124] Preferably, the upper shield layer 21 is composed of two layers,as shown in FIG. 2, so that the upper gap layer 18 and the secondupper-shield sub-layer 19 ensure the electrical insulation above theelectrode layer 17.

[0125] If the electrode layer 17 underlies the hard bias layer 16, itis, of course, preferable that the lower shield layer 20 is composed oftwo layers.

[0126]FIG. 3 is a fragmentary sectional view of a thin-film magnetichead according to a third embodiment of the present invention whenviewed from a side opposing a recording medium.

[0127] In this instance, only the lower shield layer 20 is composed oftwo layers in contrast with the second embodiment.

[0128] If the above-described magnetic materials (2) to (4), such asFeMO, FeMN, and CoMN, are used for the second lower-shield sub-layer 12,the deposited layer needs heating to form microcrystalline phases. Theheating temperature is very high and is, for example, 400° C. or more.

[0129] If the upper shield layer is composed of two layers in which thesecond upper-shield sub-layer 19 is formed of any one of theabove-described magnetic materials, the magnetic detecting element 14,which underlies the second upper-shield sub-layer 19, is likely to bemuch affected by heating.

[0130] Accordingly, if such a material that needs heating at hightemperature is used for a second shield sub-layer, only the lower shieldlayer is, preferably, composed of two layers, and following the heating,the magnetic detecting element 14 is formed.

[0131] However, some magnetic materials such as CoMO do not need heatingat high temperatures. If such a material that needs heating at arelatively low temperature, the upper shield layers may be composed oftwo layers, as shown in FIGS. 1 and 2.

[0132]FIG. 4 is a fragmentary sectional view of a thin-film magnetichead according to a fourth embodiment of the present invention whenviewed from a side opposing a recording medium. The same layers aredesignated by similar numerals.

[0133] In this embodiment, the lower shield layer 22 and the uppershield layer 23 are each composed of a monolayer. Hence, it seems tohave the same structure as the known structure, as shown in FIG. 8.

[0134] However, the structure of the fourth embodiment is different inthat the magnetic detecting element sides of the lower shield layer 22and the upper shield layer 23 each have a higher resistive area than theother sides.

[0135] In order to give a higher specific resistance to the magneticdetecting element sides of the shield layers 22 and 23, the compositionsof the shield layers 22 and 23 are changed by sputtering according tothe distance from the magnetic detecting element 14.

[0136] For example, the shield layers 22 and 23 are formed of a FeMOalloy of (2) described above using three targets of Fe, an iron oxide,an oxide of the element M

[0137] First, more power is supplied to the Fe target than to the ironoxide target and the element-M oxide target to deposit the lower shieldlayer until having a thickness of 5 ×103 Å to 3 μm. Thus, the Fe contentof the lower shield layer 22 becomes high in this area; hence the oxygencontent is low. This area of the lower shield layer 22, therefore, has arelatively low specific resistance and high soft magneticcharacteristics.

[0138] In addition, since the high Fe content leads to a large amount ofmicrocrystalline phases and a small amount of amorphous phase, it isexpected that this area is heat dissipating.

[0139] Next, power supply to the iron oxide target and the element Moxide is gradually increased to increase the oxygen content of the lowershield layer 22 as the distance from the magnetic detecting element 14is getting close. Thus, the specific resistance of the lower shieldsub-layer 22 is increased at the vicinity of the magnetic detectingelement 14. The composition ratios of FeMO in this high-oxygen-contentarea are in the range of the material (2) and the thickness of the areais set in the range of 20 to 200 Å.

[0140] On the other hand, when the upper shield layer 23 is formed,first, a lot of power is supplied to the iron oxide target and theelement M-oxide target so that the upper shield layer 23 can have a highoxygen content at the vicinity of the magnetic detecting element 14 andthus have a high specific resistance. The composition ratios of the FeMOin this high-oxygen-content area are in the range of material (2) andthe thickness of the area is set in the range of 20 to 200 Å.

[0141] Next, power supply to the Fe target is gradually increased toincrease the Fe content of the upper shield layer 23 as the distancefrom the magnetic detecting element 14 is getting longer. Thus, the softmagnetic characteristics of the upper shield layer 23 are increased inthe other area having a thickness of 5×103 to 3 μm. Since the high Fecontent leads to a large amount of microcrystalline phases and a smallamount of amorphous phase, it is expected that this area has heatdissipation performance.

[0142] The resulting lower shield layer 22 and the upper shield layer 23have high resistive areas at the vicinity of the magnetic detectingelement 14, thus improving the electrical insulation performance of thethin-film magnetic head in association with the gap layers 13 and 18. Inaddition, since the soft magnetic characteristics of the lower shieldlayer 22 and the upper shield layer 23 increase as the distances fromthe magnetic detecting element 14 is getting longer, the shieldingfunction of the shield layers 22 and 23 can be ensured. Also, since theareas far from the magnetic detecting element 14 contain a large amountof microcrystalline phases, heat dissipation performance of these areascan be improved.

[0143] The magnetic materials (1), (3), and (4) may, of course, be usedfor the shield layers 22 and 23. If FeMN alloys described in (4) areused, the shield layers 22 and 23 are formed such that the magneticdetecting element sides thereof have a specific resistance higher thanthat of the other sides while the content of the element N of thematerial is adequately adjusted.

[0144] Such a shield layer that is deposited so as to have differentcomposition ratios therein to have a higher specific resistance at thevicinity of the magnetic detecting element 14, as shown in FIG. 4, maybe formed in at least either of the lower shield layer 22 and the uppershield layer 23.

[0145] In the fourth embodiment, the entire shield layers 22 and 23 areformed by sputtering. In the first and the second embodiment, the secondshield sub-layers 12 and 19 may be formed by sputtering and the firstshield sub-layers 10 and 11 may be formed by sputtering or plating.

[0146] The multilayer film 15 of the magnetic detecting element will nowbe described. FIG. 5 is a fragmentary sectional view of the magneticdetecting element 14 according to an embodiment when viewed from a sideopposing a recording medium.

[0147] The magnetic detecting element 14 shown in FIG. 5 is a so calledsingle spin-valve thin-layer sensor.

[0148] The multilayer film 15 comprises an antiferromagnetic layer 30, apinned magnetic layer 31, a nonmagnetic conductive layer 32, and a freemagnetic layer 33, upward in that order.

[0149] The antiferromagnetic layer 30 is formed of, for example, a PtMnalloy. The pinned magnetic layer 31 comprises a magnetic layer 34, anonmagnetic interlayer 35, and a magnetic layer 36, in that order, toform a ferrimagnetic multilayer film. The magnetic layers 34 and 36 areformed of a magnetic material such as a NiFe alloy, a CoFeNi alloy, aCoFe alloy, or Co. The nonmagnetic interlayer 35 is formed of at leastone nonmagnetic material selected from the group consisting of Ru, Rh,Ir, Cr, Re, and Cu.

[0150] The magnetic moments (saturation magnetization Ms×thickness t) ofthe magnetic layers 34 and 36 are set so as to be different from eachother. For example, one magnetic layer 34 is magnetized in the directionopposite to the Y direction in the drawing and is pinned by an exchangecoupling magnetic field generated between the antiferromagnetic layer 30and the magnetic layer 34. The other magnetic layer 36 is magnetized andis pinned in the Y direction, which is opposite to the magnetization ofthe magnetic layer 34 by an exchange coupling magnetic field generatedby the RKKY interaction between the magnetic layers 34 and 36.

[0151] The free magnetic layer 30 is also a ferromagnetic multilayerfilm like the pinned magnetic layer 31. The free magnetic layer 33 iscomposed of, for example, three layers of a magnetic layer 37, anonmagnetic interlayer 38, and a magnetic layer 39.

[0152] The magnetic moments of the magnetic layers 37 and 39 aredifferent from each other. As shown in FIG. 5, a hard bias layer 40 isformed of, for example, CoPt on both sides of the magnetic layer 37 inthe track width direction, or the x direction in the drawing. Themagnetic layer 37 is oriented in the opposite direction to the xdirection by the vertical bias magnetic field from the hard bias layer40. The magnetic layer 39 is oriented in the x direction by the exchangecoupling magnetic field generated by the RKKY interaction between themagnetic layers 37 and 39, thus being pinned in the opposite directionto the magnetization of the magnetic layer 37.

[0153] As shown in FIG. 5, the hard bias layer 40 overlies an orientedlayer 41 formed of, for example, Cr and underlies an electrode layer 42formed of, for example, W or Cu.

[0154] Although the multilayer film 15 of the magnetic detecting element14 comprises the antiferromagnetic layer 30, the pinned magnetic layer31, the nonmagnetic interlayer 32, and the free magnetic layer 33,upward in that order, in this embodiment, they may be formed in theinverse order.

[0155] The pinned magnetic layer 31 and the free magnetic layer 33 donot need to be a ferrimagnetic multilayer film and may be a magneticmonolayer or multilayer film.

[0156] Although the electrode layer 42 overlies the hard bias layer 40,it may underlie the hard bias layer 40 on both sides of the multilayerfilm 15.

[0157]FIG. 6 is a fragmentary sectional view of the magnetic detectingelement 14 according to another embodiment of the present invention whenviewed from a side opposing a recording medium.

[0158] The magnetic detecting element shown in FIG. 6 is a so calledtunnel magnetoresistive sensor. While, in the magnetic detecting element14 shown in FIG. 5, the nonmagnetic conductive layer 32 is formed of anonmagnetic material such as Cu, the magnetic detecting element 14 shownin FIG. 6 has an interlayer 43 formed of an insulating material such asAl₂O₃ or SiO₂ between the pinned magnetic layer 31 and the free magneticlayer 33.

[0159] The multilayer film 15 of the magnetic detecting element 14 shownin FIG. 6 is formed between electrode layers 44. In the tunnelmagnetoresistive sensor, when a voltage is applied to the two magneticlayers, that is pinned magnetic layer 31 and the free magnetic layer 33,a tunnel current flows in the interlayer 43, thus causing a tunneleffect.

[0160] The tunnel magnetoresistive sensor is used for detecting leakagemagnetic fields from recording media in accordance with the tunneleffect principle.

[0161] In this embodiment, the multilayer film 15 is provided with thehard bias layer 40 on both sides thereof in the track width direction inthe same manner in FIG. 5. Insulating layers 45 are disposed between thehard bias layer 40 and the electrode layers 40 so that any sensingcurrent does not diverge from the electrode layers 44 into the hard biaslayer 40.

[0162] The present invention may be applied tocurrent-perpendicular-to-plane (CPP) spin-valve thin-film sensors, whichhave the same structure as shown in FIG. 6 except that the interlayer 43is formed with the nonmagnetic conductive layer 32 shown in FIG. 5.

[0163] In such a structure that has two electrode layers 44 provided onboth surfaces of the multilayer film 15, as shown in FIG. 6, preferably,the lower shield layer 20 and the upper shield layer 21 are eachcomposed of two layers, as shown in FIG. 1. Thus, higher resistivesecond shield layers 12 and 19 disposed in the magnetic detectingelement sides thereof improve electrical insulation performance.

[0164]FIG. 7 is a fragmentary sectional view of the magnetic detectingelement 14 according to another embodiment of the present invention whenviewed from a side opposing a recording medium.

[0165] The magnetic detecting element 14 shown in FIG. 7 is a so calleddual spin-valve thin-film sensor, in which nonmagnetic conductive layers32, pinned magnetic layers 31, and antiferromagnetic layers 30 aredisposed on both surfaces of the free magnetic layer 33 in that order.

[0166] The free magnetic layer 33 is composed of three layers, that is,two magnetic layers 46 formed of a CoFe alloy, Co, or the like andanother magnetic layer 47 formed of a NiFe alloy or the like. The formermagnetic layers 46 serve to prevent metallic elements from diffusingbetween the nonmagnetic conductive layers 32 and the latter magneticlayer 47, thus improving the change in resistance (ΔR) and the rate ofchange in resistance (ΔR/R). The free magnetic layer 33 may be aferrimagnetic multilayer film as shown in FIG. 5.

[0167] Also, the oriented film 41, the hard bias layer 40, and theelectrode layer 42 are provided, upward in that order, on both sides ofthe multilayer film 15 in the track width direction.

[0168] The present invention may be applied tocurrent-perpendicular-to-plane (CPP) spin-valve thin-film sensors inwhich the electrode layers 42 are disposed on both surfaces of themultilayer film 15 shown in FIG. 7. Also, the present invention may beapplied to dual tunnel magnetoresistive sensors in which the nonmagneticconductive layers 32 of the multilayer film 15 are replaced with theinsulative interlayer 43 and in which electrode layers 42 are disposedon both surfaces of the multilayer film 15.

[0169] The magnetic detecting element may be an anisotropicmagnetoresistive (AMR) sensor composed of three layers of amagnetoresistive (MR) layer formed of a NiFe alloy or the like, a shuntlayer formed of Ta or the like, and a soft adjacent layer (SAL) formedof a NiFe alloy or the like.

[0170] According to the present invention, at least one of shieldlayers, which are disposed on the gap layers on both surfaces of amagnetoresistive sensor, has a higher resistive area in the magneticdetecting element side thereof than in the other side.

[0171] Specifically, the shield layers are each composed of two layers.The second shield sub-layers disposed in the magnetic detecting elementside have a specific resistance higher than that of the first shieldsub-layers disposed in the other side Thus, the electrical insulation ofthe thin-film magnetic head can be ensured by the gap layers and thesecond shield sub-layers. Even if the thickness of the gap layers andthe gap length are decreasing, therefore, the insulation between themagnetic detecting element and the first shield sub-layers can be moreimproved.

[0172] Also, by forming the second shield sub-layers with a thin filmcapable of ensuring electrical insulation, a heat dissipating thin-filmmagnetic head can be achieved. In this magnetic head, even if thetemperature of the magnetic detecting element increases as the currentdensity is higher according to increase of the recording density, heatcan be released through the gap layers and the second shield sub-layersto the first shield sub-layers.

[0173] While the second shield sub-layers are formed of a magneticmaterial having a specific resistance higher than that of the firstshield sub-layers, the first shield sub-layers have excellent softmagnetic characteristics. By combining the first shield sub-layers withthe second shield sub-layers, the ferromagnetic bonding therebetweenimproves the soft magnetic characteristics of the second shieldsub-layers and thus the second shield sub-layers can adequately serve asshield layers in association with the first shield sub-layers.

What is claimed is:
 1. A thin-film magnetic head comprising: a magneticdetecting element; gap layers disposed on both surfaces of the magneticdetecting element; and shield layers, each disposed on the correspondinggap layer, wherein the magnetic detecting element side of at least oneshield layer has a higher specific resistance than that of the otherside.
 2. A thin-film magnetic head according to claim 1, wherein theshield layers each comprise a first shield sub-layer and a second shieldsub-layer in contact with the corresponding gap layer, and the secondshield sub-layer has a specific resistance higher than that of the firstshield sub-layer.
 3. A thin-film magnetic head according to claim 2,wherein the first shield sub-layer and the second shield sub-layer arein contact with each other.
 4. A thin-film magnetic head according toclaim 2, wherein the total thickness of the second shield sub-layer andthe gap layer adjoining the second shield sub-layer is in the range of100 to 500 Å.
 5. A thin-film magnetic head according to claim 4, whereinthe total thickness is in the range of 100 to 200 Å.
 6. A thin-filmmagnetic head according to claim 4, wherein the thickness of the secondshield sub-layer is in the range of 20 to 200 Å.
 7. A thin-film magnetichead according to claim 5, wherein the thickness of the second shieldsub-layer is in the range of 20 to 100 Å.
 8. A thin-film magnetic headaccording to claim 2, wherein the thickness of the first shieldsub-layer is in the range of 5×10³ Å to 3 μm.
 9. A thin-film magnetichead according to claim 2, wherein the second shield sub-layer comprisesa magnetic oxide.
 10. A thin-film magnetic head according to claim 9,wherein the second shield sub-layer comprises a Mn—Zn ferrite or a Ni—Znferrite.
 11. A thin-film magnetic head according to claim 9, wherein thesecond shield sub-layer comprises a magnetic material represented byFe_(a)M_(b)O_(c), wherein M represents at least one element selectedfrom the group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B,Al, Ga, Ge, and rare earth elements, and a, b, and c representing atomicratios satisfy the relationships of 50≦a≦70, 5≦b≦30, 10≦c ≦30, anda+b+c=100.
 12. A thin-film magnetic head according to claim 9, whereinthe second shield sub-layer comprises a magnetic material represented by(Co_(1-g)T_(g))_(x)M_(y)L_(z)O_(w), wherein T represents Fe or Ni; Mrepresents at least one element selected from the group consisting ofTi, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B, Al, Ga, Ge, and rare earthelements; L represents at least one element selected from the groupconsisting of Au, Ag, Cu, Ru, Rh, Os, Ir, Pt, and Pd; g representing anatomic ratio satisfies the relationship of 0≦g≦0.7 y, z, and wrepresenting atomic ratios satisfy the relationships of 3≦y≦30, 0≦z≦20,7≦w≦40, and 20≦y+z+w≦60; and x represents the atomic ratio of thebalance.
 13. A thin-film magnetic head according to claim 2, wherein thesecond shield sub-layer comprises a magnetic material represented byFe_(d)M_(e)N_(f), wherein M represents at least one element selectedfrom the group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B,Al, Ga, Ge, and rare earth elements, and d, e, and f representing atomicratios satisfy the relationships of 60≦d≦80, 10≦e≦15, 5≦f ≦30, andd+e+f=100.